Bug report

Bug summary

Plotting without colorbar gives different colors than plotting with one if all plotted values are equal. While this might be expected behaviour, I find it a bit strange. Plotting colorbar alongside the plot should only show the legend to what is plotted, not change the plot itself, I would say. We ran into this recently with geopandas geopandas/geopandas#1163 . Is this the intended behaviour of matplotlib or is it something which should be changed?

Code for reproduction

Without:
sc = plt.scatter(range(3), range(3), c=[1, 1, 1], cmap='viridis')

With:

sc = plt.scatter(range(3), range(3), c=[1, 1, 1], cmap='viridis')
plt.colorbar(sc)

Actual outcome

Expected outcome

I would expect colors to be the same in both plots above.

Matplotlib version

• Operating system: macOS
• Matplotlib version: 3.1.1
• Matplotlib backend (print(matplotlib.get_backend())): module://ipykernel.pylab.backend_inline
• Python version: 3.7.3
• Jupyter version (if applicable): 1.0.0
• Other libraries: